The story of America’s interstates is usually told as a straightforward tale of postwar progress, but the real origins are stranger and more contested than the green signs suggest. The Dwight D.

There are a number of different road designations in the United States, from highways and freeways to interstates and routes, and it can cause some confusion with different laws and regulations.

The Federal-Aid Highway Act of 1956, signed by President Dwight D. Eisenhower on June 29 of that year, funded the Interstate Highway System. Joining this transcontinental system, the Interregional ...